Process for reducing the aldehyde concentration in a mixture comprising cyclohexanone and one or more aldehydes

ABSTRACT

The invention relates to a process for reducing the aldehyde concentration in a mixture comprising cyclohexanone and one or more aldehydes, said process comprising distilling said mixture in a distillation column in the presence of an alkaline compound, wherein in the bottom of the distillation column substantially no water is present.

This application is the US national phase of international applicationPCT/NL2003/000921 filed 22 Dec. 2003 which designated the U.S. andclaims benefit of U.S. 60/436,476, dated 27 Dec. 2002 and EP 03076125.8,dated 19 Mar. 2003, the entire content of each of which is herebyincorporated by reference.

The invention relates to a process for reducing the aldehydeconcentration in a mixture comprising cyclohexanone and one or morealdehydes.

Such a process is known from GB-A-2028329. This patent publicationdescribes that aldehydes like caproaldehyde (hexanal) can be removed bysubjecting a mixture comprising cyclohexanone and aldehydes to an aldolcondensation reaction carried out in a separate aldol condensationvessel in the presence of an aqueous sodium hydroxide solution. Theso-obtained mixture is subsequently washed with water to remove sodiumhydroxide. In order to improve phase separation, cyclohexane is fed tothe washing device. The washed organic mixture is subsequently distilledin a distillation column where low boiling components are distilled off.

A disavantage of the process as described in GB-A-2028329 is that aseparate aldol condensation reaction vessel and a washing device areneeded. Another disadvantage is that in case the washing is effected inthe presence of cyclohexane, cyclohexane has to be removed from thewashed mixture.

The object of the present invention is to provide a simple and efficientprocess for removing aldehydes from cyclohexanone.

This object is achieved in that the process comprises distilling themixture comprising cyclohexanone and one or more aldehydes in adistillation column in the presence of an alkaline compound, wherein inthe bottom of the distillation column substantially no water is present.

Using the process of the invention cyclohexanone can be obtained havinga purity with respect to aldehydes which is at least comparable to thepurity of the cyclohexanone as obtained in the process as described inGB-A-2028329. Using the process of the present invention cyclohexanonehaving an increased purity with respect to aldehyde content can beobtained in a very simple manner. An advantage of the process of theinvention is that a separate aldol-condensation reaction vessel and awashing device are not necessary. An additional advantage is that waterand optionally cyclohexane which is/are added in the washing stepdoes/do not have to be removed. This is advantageous because lessprocess equipment is necessary and less energy is necessary to obtaincyclohexanone with sufficient purity with respect to aldehydes.

Aldehydes may for example be formed during the preparation ofcyclohexanone. Examples of aldehydes are butanal, pentanal and hexanal.Said aldehydes include aldehydes which could hardly be separated fromcyclohexanone under conventional distillation conditions. Aldehydeswhich could hardly be separated under conventional distillationconditions in particular concerns pentanal and hexanal. The presence ofthese aldehydes, and especially the presence of pentanal and hexanal, incyclohexanone is undesired. In particular when cyclohexanone having atoo high concentration of pentanal and hexanal (relative to the mixturecomprising cyclohexanone, hexanal and/or pentanal) is processed intopolycaprolactam (nylon-6) by oximation, Beckmann rearrangement andpolymerization, the mechanical strength of the polycaprolactam obtainedmay be decreased to an undesired extent. When such cyclohexanone isprocessed into polycaprolactam, the aldehydes and especially pentanaland hexanal, even if present in low concentrations, give rise toimpurities having a highly deleterious effect on the strength of thepolycaprolactam. It has been found that the concentration of pentanaland hexanal in cyclohexanone is preferably lower than 90 weight ppm(relative to the mixture comprising cyclohexanone, pentanal andhexanal). The term weight ppm (parts per million) pentanal and hexanalis understood to mean the ratio of grams of the pentanal and hexanal perone million gram of the mixture comprising cyclohexanone, pentanaland/or hexanal.

In the process of the present invention, no or substantially no water ispresent in the bottom of the distillation column. As used herein,substantially no water means in particular that less than 100 weight ppmof water is present in the bottom of the distillation column (relativeto the bottom product, i.e. the mixture present in the bottom of thedistillation column contains less than 100 weight ppm of water). Theterm weight ppm (parts per million) water is understood to mean theratio of grams of water per one million gram of bottom product. It hassurprisingly been found that when the distilling is performed in thepresence of less than 100 weight ppm of water in the bottom, the amountof aldehydes and in particular the amount of pentanal and hexanal can bedecreased to very low values, even to below 90 weight ppm.

The presence of less than 100 weight ppm of water in the bottom of thedistillation column can be obtained in any suitable way. Preferredmethods are described in the present disclosure.

The process of the present invention is performed in a distillationcolumn. The column may be any suitable distillation column. Examples ofsuitable distillation columns are tray columns or columns filled with arandom or structured packing. The bottom of a distillation column isknown to a person skilled in the art and refers in particular to thezone in which the liquid phase is present which is the most rich inhigh-boiling components, for example, the reboiler zone and the zonebelow the lowest tray for a tray distillation column and the reboilerzone and the zone below the packing for a distillation column filledwith a packing.

The distillation may be carried out at any suitable temperature. Thedistillation is preferably carried out at a top temperature of between45 and 130° C. and at a bottom temperature of between 105 and 190° C.The pressure applied at the top of the distillation column is in generalbetween 0.02 and 0.15 MPa.

In the process of the invention, the mixture comprising cyclohexanoneand aldehydes is distilled in the presence of an alkaline compound.Preferably, the mixture comprising cyclohexanone and aldehydes isdistilled with an effective amount of alkaline compound to lower theconcentration of pentanal and hexanal to such an extent that theconcentration of pentanal and hexanal in the cyclohexanone is lower than90 weight ppm.

Any suitable alkaline compound may be used. Suitable alkaline compoundsinclude any alkaline compound capable of effecting aldol condensation ofone or more of the aldehydes present in the mixture to be distilled, inparticular of pentanal and hexanal. The alkaline compound is preferablyan alkali metal compound. Preferred alkaline compounds are alkali metalhydroxide, alkali metal carbonates and alkali metal alkoxides. Thealkali metal may be sodium, preferably potassium. In case an alkalimetal compound is used, distilling the mixture comprising cyclohexanoneand one or more aldehydes is preferably effected with such an amount ofalkali metal compound that the concentration of alkali metal in thebottom of the distillation column is higher than 2 weight ppm and lowerthan 50 weight ppm. When more than 2 weight ppm of alkali metal ispresent in the bottom of the distillation column the amount of aldehydesand especially the amount of pentanal and hexanal in the cyclohexanonelowers to an increased extent. Using less than 50 weight ppm of alkalimetal in the bottom of the distillation column is found to avoid orreduce loss of cyclohexanone.

The alkaline compound may be introduced in the mixture prior to feedingthe mixture to the distillation column or it may be directly introducedto the distillation column. Preferably, the alkaline compound isintroduced to the distillation column at the level where the mixture tobe distilled in the distillation column is fed or in the zone below thislevel because this results in a decrease of cyclohexanone loss. Thealkaline compound is preferably present in a mixture which is fed to thedistillation column and more preferably in the mixture comprisingcyclohexanone and one or more aldehydes to be distilled with the processof the present invention

The alkaline compound may be fed to the distillation column in anysuitable way, usually as a liquid. Preferably, the alkaline compound isfed to the distillation column by using a solution comprising water andthe alkaline compound (hereinafter referred to as aqueous solutioncomprising the alkaline compound).

It has been found that in case an aqueous solution comprising thealkaline compound is used, said aqueous solution is advantageously fedto the distillation column at a level above the bottom of thedistillation column. This is an advantage way to achieve thatsubstantially no water is present in the bottom of the distillationcolumn. In case a tray distillation column is used, said aqueoussolution is advantageously fed to or above the first (numbered from thebottom of the distillation column to the top) tray of the distillationcolumn. In case a packed distillation column is used, said aqueoussolution is advantageously fed at a level where the packing is present.

Feeding the aqueous solution comprising the alkaline compound to thedistillation column is preferably effected by feeding the aqueoussolution comprising the alkaline compound directly to the distillationcolumn at a level above the bottom of the distillation column and/or byfeeding the aqueous solution comprising the alkaline compound to amixture which is fed to the distillation column at a level above thebottom of the distillation column. The process according to theinvention preferably comprises feeding the mixture comprisingcyclohexanone and one or more aldehydes to the distillation column at alevel above the bottom of the distillation column. The aqueous solutioncomprising the alkaline compound is preferably fed to the mixturecomprising cyclohexanone and one or more aldehydes prior to feeding themixture comprising cyclohexanone and one or more aldehydes at a levelabove the bottom of the distillation column.

Particularly suitable aqueous solutions are aqueous solutions of alkalimetal hydroxides, alkali metal carbonates, alkali metal alkoxides inparticular alkali metal cyclohexanolate. When the aqueous solution isfed directly to the distillation column or when the aqueous solution isfed to the mixture comprising cyclohexanone and one or more aldehydes,the aqueous solution preferably contains from 0.5 to 50 wt. %, more inparticular from 5 to 45 wt. % of the alkali metal compound, preferablyof sodium hydroxide, most preferably of potassium hydroxide.

In particular, the amount of aqueous potassium hydroxide solutiondirectly introduced in the distillation column or in the mixture priorto feeding the mixture to the distillation column is preferably suchthat at least 2 weight ppm and more preferably at least 5 weight ppm ofpotassium is present in the bottom of the distillation column because byusing less than 2 weight ppm of potassium in the bottom of thedistillation column the amount of aldehydes and especially the amount ofpentanal and hexanal in the cyclohexanone lowers to a lesser extent. Theamount of aqueous solution of potassium hydroxide introduced into thedistillation column is preferably such that that the amount of potassiumin the bottom of the distillation column is not higher than 50 weightppm and more preferably not higher than 40 weight ppm and even morepreferred not higher than 35 weight ppm because it has been found thatthe use of more than 35 weight ppm of potassium in the bottom of thedistillation column results in an increased loss of cyclohexanone.

The mixture comprising cyclohexanone and one or more aldehydes which isdistilled in the process of the invention can be obtained with variousknown processes. The mixture usually comprises more than 200 weight ppmof aldehydes and less than 6000 weight ppm of aldehydes (relative to themixture). The mixture usually comprises more than 500 weight ppm andless than 5000 weight ppm pentanal and hexanal (relative to themixture).

Preparing of the mixture, for example, involves oxidizing cyclohexane inthe liquid phase with an oxygen containing gas in the presence orabsence of an oxidation catalyst. In one embodiment of the invention,preparing the mixture involves oxidizing cyclohexane in the presence ofan oxidation catalyst resulting in an oxidized mixture comprisingcyclohexane, cyclohexanone and cyclohexanol, and typically also low andhigh boiling compounds.

In another and preferred embodiment of the invention, preparing themixture involves oxidizing cyclohexane in the absence of an oxidationcatalyst resulting in an oxidation mixture comprising cyclohexane,cyclohexyl hydroperoxide, cyclohexanone and cyclohexanol andsubsequently treating this mixture with a cyclohexylhydroperoxide-decomposing metal salt in the presence of an aqueoussolution of an alkali metal hydroxide to effect decomposition of thecyclohexyl hydroperoxide into cyclohexanone and cyclohexanol to obtain amixture comprising cyclohexane, cyclohexanone, cyclohexanol, andtypically also low boiling and high boiling components. In oneembodiment, the mixture comprising cyclohexane, cyclohexanone andcyclohexanol is distilled in the presence of an alkaline compoundaccording to the invention. In another and more preferred embodiment,preparing of the mixture further involves separating cyclohexane fromthe mixture comprising cyclohexane, cyclohexanone and cyclohexanol toobtain the mixture to be distilled in the presence of an alkalinecompound according to the invention. The process of the presentinvention therefore also relates to a process comprising oxidizingcyclohexane in the liquid phase with an oxygen containing gas, resultingin an oxidation mixture comprising cyclohexane, cyclohexylhydroperoxide, cyclohexanone and cyclohexanol; treating the oxidationmixture with a cyclohexyl hydroperoxide decomposing metal salt in thepresence of an alkali metal hydroxide such as to effect decomposition ofthe cyclohexyl hydroperoxide into cyclohexanone and cyclohexanol,resulting in a mixture comprising cyclohexanone, cyclohexanol andcyclohexane; separating, by distillation, cyclohexane from the mixturecomprising comprising cyclohexanone, cyclohexanol and cyclohexane;separating, by distillation, low boiling compounds from the resultingmixture to obtain a top product comprising low boiling compounds and abottom product comprising cyclohexanone, cyclohexanol and high boilingcompounds; and effecting the distillation to separate cyclohexane or thedistillation to separate low boiling compounds in the presence of analkaline compound in a distillation column, wherein in the bottom of thedistillation column substantially no water is present. This specificcombination of steps was found to result in cyclohexanone having anextremely low concentration of aldehydes, in particular of pentanal andhexanal, without having to use a separate aldol condensation step andwashing step. With low boiling compounds is meant compounds having aboiling point lower than cyclohexanone and higher than cyclohexane.Examples are butanol, pentanal, hexanal, pentanol and epoxy cyclohexane.With high boiling compounds is meant compounds having a boiling pointhigher than cyclohexanol. Examples are 2-cyclohexylidene cyclohexanone,2-hexylidene cyclohexanone and 2-(cyclohexen-1-yl)cyclohexanone. InEP-A-579323 an exemplary process is described for oxidizing cyclohexanein the absence of an oxidation catalyst resulting in an oxidationmixture comprising cyclohexane, cyclohexyl hydroperoxide, cyclohexanoneand cyclohexanol. In GB-A-1382849 and EP-A-4105 exemplary processes aredescribed for treating a mixture comprising cyclohexane, cyclohexylhydroperoxide, cyclohexanone and cyclohexanol with a cyclohexylhydroperoxide-decomposing metal salt in the presence of an aqueoussolution of an alkali metal hydroxide to effect decomposition of thecyclohexyl hydroperoxide into cyclohexanone and cyclohexanol.

The oxidized mixture or mixture obtained after decomposition is usuallyprocessed by first distilling off cyclohexane and the by-products thatare more volatile than the cyclohexane, followed by distilling off lowboiling compounds, subsequently cyclohexanone and finally thecyclohexanol. Cyclohexanol may subsequently subjected to adehydrogenation reaction using a dehydrogenator. In one embodiment ofthe invention, the process of the present invention is performed in adistillation column in which cyclohexane is distilled off. Preferably,the process of the present invention is performed in a distillationcolumn in which low boiling components are separated from a mixture alsocontaining cyclohexanone, cyclohexanol, and high boiling compounds toobtain a top product comprising low boiling compounds and a bottomproduct comprising cyclohexanone, cyclohexanol and high boilingcompounds. A preferred embodiment of the present invention thereforerelates to a process to distill off low boiling components from amixture also comprising cyclohexanone, cyclohexanol and high boilingcompounds, said mixture also including hexanal and/or pentanal, in thepresence of an alkaline compound in a distillation column in which inthe bottom no or substantially no water is present. Usually, the mixturewhich is fed to the distillation column in which low boiling componentsare distilled off, comprises between 40 and 60 wt. % cyclohexanone,between 40 and 60 wt. % cyclohexanol, typically between 0.2 and 2 wt. %low-boiling compounds and typically between 1 and 4 wt. % high boilingcompounds and typically between 200 and 6000 weight parts per million ofaldehydes, in particular 500-5000 weigth ppm hexanal and pentanal.

The process of the invention will now be further elucidated with thefollowing non-limiting examples.

Experiment A

A mixture, comprising cyclohexanone, cyclohexanol and low and heavyboiling compounds was fed to a first distillation column at a rate of 25m³/hr. Pentanal and hexanal concentrations in the mixture were 70 and300 weight ppm respectively. The mixture was fed to the 23^(rd) tray ofthe total 60 sieve trays (trays numbered from bottom to top). The columnwas operated at 0.08 MPa and 121° C. at the top of the column and about0.1 MPa at tray with number 20 and 165° C. at the bottom of the column.14 t/h steam (1.25 MPa) was applied in the reboiler. Low boilingproducts, such as n-butanol, n-pentanol, hexanal and epoxy cyclohexanewere separated off via the top of the column. An aqueous solution of 5wt % KOH was added to the bottom of the distillation column at a rate of50 ml/min, resulting in a water concentration of 150 weight ppm and apotassium concentration of 5 weight ppm in the bottom product. Thebottom product was withdrawn from the distillation column and mixed witha 25 m³/hr mixture of cyclohexanone, cyclohexanol and heavy boilingcomponents. This mixture was fed to the top of a second distillationcolumn. The second column is a packed column and operates atapproximately 74° C. at the top of the column; and 10.7 kPa at 103° C.at the bottom of the column. Cyclohexanol and heavy boiling componentsleft the bottom of the second distillation column. The pentanal andhexanal concentrations in the top product (mainly comprisingcyclohexanone) were 12 and 130 weight ppm respectively Concentration ofCHIA (2-cyclohexylidene cyclohexanone which is a dimer of cyclohexanone)in the bottom of the first distillation column was 0.1 wt. %, indicatingthat product losses due to dimerization of cyclohexanone were small.

Comparative Experiment B

Experiment A was repeated with the difference that pentanal and hexanalconcentrations in the feed of the first distillation column were 400weight ppm and 2100 weight ppm. No aqueous KOH solution was fed to thefirst distillation column. The pentanal and hexanal concentrations inthe top product (mainly comprising cyclohexanone) of the second columnwere 20 and 190 weight ppm respectively (relative to the cyclohexanonepresent in the top product). Concentration of CHIA (2-cyclohexylidenecyclohexanone) in the bottom of the first distillation column was 0.1wt. %, indicating that product losses due to dimerization ofcyclohexanone were small.

Experiment C

A mixture of cyclohexanone, cyclohexanol, low and heavy boilingcompounds, 400 weight ppm pentanal and 2100 weight ppm hexanal, wastreated with 2.5 m³/hr NaOH solution, having an alkalinity of 2 meq/g,in a stirred saponification vessel at a rate of 25 m³/hr at 103° C.during 15 minutes. The resulting mixture was mixed with 20 m³/hrcyclohexane and sent to a separation vessel to separate the aqueousphase. The organic mixture was countercurrently washed in a packedcolumn with 7 m³/hr water to extract the water droplets containingsodium. The washed organic mixture was sent to the top of a dryingcolumn to remove cyclohexane and water. The drying column had 15 sievetrays and was operated at a pressure of about 0.1 MPa, a top temperatureof about 78° C., and a bottom temperature of about 161° C. Pentanal andhexanal concentrations in the bottom product of the drying column were70 and 300 ppm. Comparative Experiment B was repeated with this bottomproduct as feedstock, resulting in pentanal and hexanal concentrationsin the top product of the second column of 6 and 60 weight ppmrespectively (relative to the cyclohexanone present in the top product).Concentration of CHIA (2-cyclohexylidene cyclohexanone) in the bottom ofthe first distillation column was 0.1 wt. %, indicating that productlosses due to dimerization of cyclohexanone were small.

EXAMPLE I

Experiment A was repeated with the difference that the 50 ml/min 5 wt. %KOH solution was fed in the feed pipe of the first distillation column.Potassium concentration in the bottom was 5 weigth ppm (hereinafterreferred to as ppmw) and the water concentration in the bottom was <10ppmw. The pentanal and hexanal concentrations in the top product of thesecond column were 4 and 50 ppmw respectively (relative to thecyclohexanone present in the top product). Concentration of CHIA(2-cyclohexylidene cyclohexanone) in the bottom of the firstdistillation column was 0.07 w %.

Comparison of Example I with Experiment C indicates that with theprocess of the invention cyclohexanone with an even increased puritywith respect to pentanal and hexanal can be obtained in a very simplemanner.

EXAMPLE II

Example I was repeated with the difference that the KOH solution flowrate was increased to 70 ml/min. Potassium concentration in the botttomwas 7 ppmw and water concentration in the bottom was <10 ppmw. Thepentanal and hexanal concentrations in the top product of the secondcolumn were 2 and 15 ppmw respectively (relative to the cyclohexanonepresent in the top product). Concentration of CHIA (2-cyclohexylidenecyclohexanone) in the bottom of the first distillation column was 0.10wt %.

Example III

Example I was repeated with the difference that the KOH solution flowrate was increased to 350 ml/min. Potassium concentration in the bottomwas 35 ppmw and water concentration in the bottom was <10 ppmw. Thepentanal and hexanal concentrations in the top product of the secondcolumn were 1 and 5 ppmw respectively (relative to the cyclohexanonepresent in the top product). Concentration of CHIA (2-cyclohexylidenecyclohexanone) in the bottom of the first distillation column was 0.35wt %.

1. Process for reducing the aldehyde concentration in a mixturecomprising cyclohexanone and one or more aldehydes comprising: oxidizingcyclohexane in a liquid phase with an oxygen containing gas resulting inan oxidation mixture comprising cyclohexane, cyclohexyl hydroperoxide,cyclohexanone and cyclohexanol; treating the oxidation mixture with acyclohexyl hydroperoxide decomposing metal salt in the presence of analkali metal hydroxide such as to effect decomposition of the cyclohexylhydroperoxide into cyclohexanone and cyclohexanol, resulting in amixture comprising cyclohexanone, cyclohexanol and cyclohexane;separating, by a first distillation, cyclohexane from the mixturecomprising cyclohexanone, cyclohexanol and cyclohexane to thereby obtaina resulting mixture comprising cyclohexanone and cyclohexanol; andseparating, by a second distillation, low boiling compounds from theresulting mixture comprising cyclohexanone and cyclohexanol to obtain atop product comprising low boiling compounds and a bottom productcomprising cyclohexanone, cyclohexanol and high boiling compounds;wherein the process further comprises reducing the aldehydeconcentration in the mixture comprising cyclohexanone and one or morealdehydes by carrying out at least one of the first and seconddistillations in a distillation column in the presence of an alkalinecompound, wherein less than 100 weight ppm of water is present in thebottom of the distillation column.
 2. Process according to claim 1,wherein the process further comprises feeding said bottom product toanother distillation column in which cyclohexanone is distilled off as atop product.
 3. Process according to claim 1, wherein the resultingmixture from the first distillation comprises cyclohexanone,cyclohexanol, low boiling compounds and high boiling compounds andwherein the distilling in the second distillation involves separation oflow boiling compounds to obtain a top product comprising low boilingcompounds and a bottom product comprising cyclohexanone, cyclohexanoland high boiling compounds.
 4. Process according to claim 1, wherein thealdehydes are hexanal and/or pentanal.
 5. Process according to claim 1,wherein the second distillation column is operated at a top temperatureof between 45 and 130° C. and a bottom temperature of between 105 and190° C.
 6. Process according to claim 1, wherein the process comprisesfeeding a solution comprising water and the alkaline compound to thedistillation column at a level above the bottom of the distillationcolumn.
 7. Process according to claim 1, wherein the process comprisesfeeding the mixture resulting from the decomposition treatment of theliquid phase cyclohexane oxidation to said distillation column andfeeding a solution comprising water and the alkaline compound to thedistillation column at a level above the bottom of the distillationcolumn.
 8. Process according to claim 1, wherein the process comprisesfeeding the mixture to the distillation column at a level above thebottom of the distillation column and introducing a solution comprisingwater and the alkaline compound into the mixture prior to said feeding.9. Process according to claim 1, wherein the alkaline compound is analkali metal compound.
 10. Process according to claim 9, wherein thedistillation column is operated with an amount of alkali metal compoundsuch that the concentration of alkali metal in the bottom of thedistillation column is higher than 2 weight ppm and lower than 50 weightppm.
 11. Process according to claim 1, wherein the alkaline compound isan alkali metal hydroxide, alkali metal carbonate or alkali metalalkoxide.
 12. Process according to claim 1, wherein the alkalinecompound is sodium hydroxide or potassium hydroxide.
 13. Processaccording to claim 1, which further comprises feeding the bottom productof the second distillation to a distillation column in whichcyclohexanone is distilled off as a top product.
 14. Process forreducing the aldehyde concentration in a mixture comprisingcyclohexanone and one or more aldehydes, the process comprising:oxidizing cyclohexane in a liquid phase with an oxygen containing gas inthe absence of an oxidation catalyst resulting in an oxidation mixturecomprising cyclohexane, cyclohexyl hydroperoxide, cyclohexanone andcyclohexanol; treating the oxidation mixture with a cyclohexylhydroperoxide decomposing metal salt in the presence of an alkali metalhydroxide such as to effect decomposition of the cyclohexylhydroperoxide into cyclohexanone and cyclohexanol to obtain a mixturecomprising cyclohexanone and one or more aldehydes; and reducing thealdehyde concentration in the mixture by distilling the mixture in adistillation column in the presence of an alkaline compound, whereinless than 100 weight ppm of water is present in the bottom of thedistillation column.
 15. Process according to claim 14, furthercomprising separating cyclohexane from the mixture prior to distilling.16. Process according to claim 14, wherein the mixture resulting fromthe decomposition treatment of the liquid phase cyclohexane oxidationcomprises cyclohexanone, cyclohexanol, low boiling compounds and highboiling compounds and wherein said distilling involves separation of lowboiling compounds to obtain a top product comprising low boilingcompounds and a bottom product comprising cyclohexanone, cyclohexanoland high boiling compounds.
 17. Process according to claim 14, whereinthe aldehydes are hexanal and/or pentanal.
 18. Process according toclaim 14, wherein the distillation column is operated at a toptemperature of between 45 and 130° C. and a bottom temperature ofbetween 105 and 190° C.
 19. Process according to claim 14, wherein theprocess comprises feeding a solution comprising water and the alkalinecompound to the distillation column at a level above the bottom of thedistillation column.
 20. Process according to claim 14, wherein theprocess comprises feeding the mixture resulting from the decompositiontreatment of the liquid phase cyclohexane oxidation to said distillationcolumn and feeding a solution comprising water and the alkaline compoundto the distillation column at a level above the bottom of thedistillation column.
 21. Process according to claim 14, wherein theprocess comprises feeding the mixture to the distillation column at alevel above the bottom of the distillation column and introducing asolution comprising water and the alkaline compound into the mixtureprior to said feeding.
 22. Process according to claim 14, wherein thealkaline compound is an alkali metal compound.
 23. Process according toclaim 22, wherein the distillation column is operated with an amount ofalkali metal compound such that the concentration of alkali metal in thebottom of the distillation column is higher than 2 weight ppm and lowerthan 50 weight ppm.
 24. Process according to claim 14, wherein thealkaline compound is an alkali metal hydroxide, alkali metal carbonateor alkali metal alkoxide.
 25. Process according to claim 14, wherein thealkaline compound is sodium hydroxide or potassium hydroxide. 26.Process according to claim 14, which further comprises feeding thebottom product to a distillation column in which cyclohexanone isdistilled off as a top product.